Thermal Fatigue Assessment for Penetration Flow into a Branch Pipe of Mixing Tee
Abstract
Thermal fatigue cracks may be initiated at T-junction pipes where high- and low-temperature fluids flow in and mix. The authors previously conducted visualization studies of flow fields in a T-junction pipe. As a result, flows from the main pipe penetrated into the branch line intermittently depending on the momentum ratio between main and branch lines. In the present study, numerical simulations were carried out to reproduce flow fields observed in the visualization studies and estimate the temperature on the inner surface of the blanch line. The large eddy simulation (Dynamic Smagorinsky) was carried out. Inner diameters were Dm = 60 mm (main) and Db = 20 mm (branch). The simulation results of the maximum penetration depth for experimental conditions were agreed well with experimental data quantitatively. Temperature fluctuation appeared on the inner surface of the branch line. As the momentum ratio increased, the peak value of the temperature fluctuation appeared at the deeper point on the branch inner surface. When the temperature difference between the main and branch pipes increased from 30°C to 150°C, the simulation results of the maximum penetration depth increased by a factor of 1.2 to 1.5. The possible reasons were increase of the buoyancy and the decrease of the viscosity which caused the decrease of the wall friction.